The present invention relates to a method and apparatus for verifying the seismic integrity of leads of an electronic component. More specifically, the present invention relates to a method and apparatus which can be utilized to determine whether or not certain aged electrical components, i.e., components which have been installed in an electrical circuit for a number of years, have sufficient lead integrity to withstand a seismic event, particularly such electrical components which have been installed in nuclear power plants.
The aging of electronic components, i.e., resistors, capacitors, etc. and the effect of such aging on the integrity of the component during a seismic event, i.e., an earthquake, has not been well studied to date. However, the aging of electronic components, and the integrity of same, is of significant importance to safety systems installed in various type plants, particularly nuclear power plants, because an aging mechanism must not degrade an electronic component to a point where a common mode failure of redundant systems can occur during an earthquake.
As a result of the tests conducted to determine if aged electrical or electronic components will maintain their electrical integrity when subjected to seismic stresses, component lead failure is a predominant failure mode observed in those few components not capable of potentially surviving a seismic event. That is, it has been found that one of the recurring failure modes given for components subjected to seismic stress is the separation of the lead from the component body. Moreover, it appears that this lead failure appears to be isolated to individual specific components, and not generic to any family of components. Consequently, there is a problem in determining just how to detect such component lead failure, particularly with regard to components which are already installed in operating systems.
One way to detect component lead failure is to seismically test equipment which has been installed in an operating system, particularly in a nuclear power plant, for say ten years. This manner of testing, however, is not practical, because such testing can deteriorate the equipment to where its ability or capability to withstand any further earthquake induced force is questionable. A further testing alternative is to periodically conduct accelerating aging and seismic testing on a wide range of electronic components so as to attempt to detect this lead integrity failure phenomenon in advance. However, the results gathered by such a testing program would clearly not apply to equipment which uses components procured and installed several years before. Consequently, it appears that in order to test the lead integrity of components already installed, it is necessary to periodically check the component leads with a meaningful test which will determine their integrity.